As a vehicle braking apparatus, there is a known electronically controlled braking apparatus for electrically controlling a braking force of the vehicle, i.e., hydraulic pressure supplied to wheel cylinders for which braking forces are to be generated in response to a brake operating force or a brake operation amount input from a brake pedal. As this electronically controlled braking apparatus, there is a known ECB (Electronically Controlled Brake) that controls the braking forces by setting target braking hydraulic pressure according to the brake operation amount, regulating the hydraulic pressure accumulated in an accumulator, and then supplying the hydraulic pressure to the wheel cylinders.
The ECB includes a master cylinder actuated in response to brake pedal operation by a driver, a stroke simulator coupled to the master cylinder, a master cut valve provided in a hydraulic path for connecting the master cylinder and the brake wheel cylinders, the accumulator capable of accumulating the hydraulic pressure, and a pressure regulating mechanism for regulating the hydraulic pressure accumulated in the accumulator. Therefore, if the driver depresses the brake pedal, the master cylinder generates the hydraulic pressure according to the operation amount and part of hydraulic oil flows into a stroke simulator to absorb a brake pedal stroke and apply a brake reaction force to the brake pedal to thereby regulate the operation amount of the brake pedal. On the other hand, a brake ECU sets a target braking force, i.e., target braking hydraulic pressure for the vehicle according to the brake operation amount and the pressure regulating mechanism regulates the hydraulic pressure of the accumulator and supplies it to the respective wheel cylinders and, as a result, it is possible to obtain the braking force desired by the occupant.
In the ECB described above, appropriate braking hydraulic pressure is supplied to the respective wheel cylinders by setting appropriate target braking hydraulic pressure according to the brake operation input from the brake pedal and electrically controlling the pressure regulating mechanism to regulate the pressure. Therefore, when a power supply unit fails, the pressure regulating mechanism cannot be controlled and it becomes difficult to supply the appropriate hydraulic pressure to the respective wheel cylinders. Therefore, as a unit for normally actuating the electronically controlled apparatus such as the braking apparatus even when the power supply unit fails, there is a power supply unit for a vehicle described in Patent Document 1, for example.
The power supply unit for the vehicle described in the Patent Document 1 is composed of a power supply backup unit using a capacitor unit formed with a plurality of capacitors as an auxiliary power supply and includes an electric power supply section for enabling supply of electric power from the capacitor unit even when a battery is normal and a forcible actuation section for actuating the electric power supply section, and the operating state of the electric power supply section is checked when the battery is normal.